Bigleaf hydrangeas are one of my favorite ornamentals. When I was a child, my great-aunt had many in her yard. My name for them back then was “blue ball bushes,” because almost all of her hydrangeas had big, blue flower clusters.
University of Georgia Horticulturist Gary Wade says there are more than 500 known cultivars of bigleaf hydrangeas. There are two main group; hortensias, which have the large, round flower clusters, and lacecapes, which have mostly flat-top flowers. Bigleaf hydrangeas prefer morning sun and afternoon shade. They also prefer well-drained soils. Bigleaf hydrangeas make excellent container plants. Growing them in containers can be beneficial because their buds can be sensitive to cold damage.
As many of you may know, adjusting the pH of the soil changes the flower color, but it is actually the presence of aluminum that causes the color change. As the pH of the soil becomes more acidic (lower pH), aluminum is more available to the plant, causing the flowers to be blue. As the pH of the soil become more alkaline (higher pH), aluminum is less available to the plant, causing the flowers to be pink. Wade says a quick way to change the flower color is through soil drenches. One tablespoon of aluminum sulfate per gallon of water drenched around the plant during the spring will change the flower color to blue. If you want to quickly change the flower color to pink, dissolve one tablespoon of hydrated lime per gallon of water and drench around the plant in the spring.
Bigleaf hydrangeas flower on the previous year’s growth. Because of this pruning should happen right after flowering. New flowers begin to form in late summer, pruning any time after that can affect the next year’s flowers. If you have winter damage, go ahead and prune out the dead plant material. Not only does this improve the overall look of the hydrangea, but it is also improves the health.
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Bigleaf hydrangeas are susceptible to powdery mildew and fungal leaf spot. While rarely will either one actually kill a hydrangea, they will affect the overall appearance and health of the plant. With disease, proper irrigation, fertilization and sanitation is important. If fungicides are to be applied they should be applied when conditions are favorable for the disease, usually humid weather. For more information on fungicides and disease identification, contact your extension office.
Aphids can be a pest on hydrangeas. Aphids can usually be kept at bay by biological controls depending on their populations. Aphids excrete honeydew, which sooty mold grows on. The honeydew will also attract ants. Mites can also be a pest on hydrangeas. Mites are too small to see with your naked eye but will cause the leaves to be distorted. The best way to prevent mites is adequate watering because they thrive in hot, dry weather.
Iron chlorosis can be an issue in bigleaf hydrangeas. As pH increases, iron becomes less available to the plant. Adding iron chelate can solve the problem, but as long as the soil pH remains high it will need to be reapplied.
I hope this information has encouraged you to plant bigleaf hydrangeas or has increased the love of the ones that you already have.
For more information on any program area, contact Houston County Extension at 478-987-2028 or drop by our office in the old courthouse, downtown Perry, 801 Main St. Office hours are 8 a.m.-5 p.m., Monday through Friday. Visit our website at http://www.caes.uga.edu/extension/houston/ for more news about your local Extension office.